OPTICAL DISKS
CD data is stored on a 4.75-inch polymer disk. To create a music CD, a medium-powered laser is used to burn millions of microscopic pits into the substrate of a master disk.
Additional copies of a CD can then be "pressed" or "stamped" in a process similar to the one used to make those old vinyl records you've heard your parents (or grandparents) talk about.
There are really three layers to a CD
- The clear plastic polymer
- A metallic backing
- A protective plastic top layer.
Care should be taken with BOTH sides of the disk
You should clean the bottom of the disk from the center out using a soft moist cloth.
- Moves crud to the outside not around the disk
- Any scratches are across the track not along it
CD / CDR / CDRW
Optical storage for computers now comes in many flavors. We now have the ability to read, write and read/write onto optical medium.
Structure
- Unlike magnetic medium, an optical storage track is a spiral
- Data is written from the "inside out
Speed Thrills
As CD-ROM technology improved so did CD-ROM speed. First there were double speed drives, then triple, then quad. And then, well, up.
Don’t be confused by the word "speed" here. It doesn’t refer directly to how fast the disk spins; here it refers to a data transfer rate (DTR) that is some multiple of the original 150K/sec audio requirement.
Thus, a double-speed drive (2x) would transfer data at 300KB (2 times 150K/sec), a quad-speed (4x) 600K/sec. There have been drives on the consumer market of up to 72-speed (72x). This drive would transfer data at a rate of a whopping 10,800KBs!
Note that x-speeds only matter with computer data transfer and do not affect sound or video! 1x is fine for both sound and video.
Note that DVD drives have an 1x-speed of 1039K/sec.
CLV (Constant Linear Velocity)
- Drives earlier than about 10X
- Data is read at a constant data rate
- Drive spins faster in the center of disk and slower at the outside
CAV (Constant Angular Velocity)
- Used on modern drives
- Drive spins at consistent speed
- Data is read at a variable data rate – fastest on the outside
- Drives use buffer chips to even out data access
Writing CDs
| Type | Writes | Media |
| CD R |
100 yr |
Write once to any specific location. On a multisession disc, you lose about 23MB of space when the first session is closed, and about 14MB for each subsequent session. |
| CD RW | 25 yr | Read, write. |
DVD (Digital ? Disk)
Capacities
DVDs achieve their high capacity by packing their bits tighter (by using a different frequency laser), using multiple "layers" and using both sides of the medium.
Single-sided, single layer (4,7GB)
Single-sided, double layer (8,5GB)
Double-sided, double layer (17GB)
Computer Formats - http://www.dvddemystified.com/dvdfaq.html#4.3
Writing DVDs (the return of VHS & BETA)
| Type | Writes | Media |
| DVD RAM | 100,000 | Historically cartridge based. Newer models may be disk based. Least compatible with set top boxes. RAM = quick access. Error free, long term. |
| DVD -RW | 1000 | A - Authoring. G - General use. Fairly compatible with set top boxes. 4x RW. 8X R. Cheap media |
| DVD +RW | 1000 | Fastest write speeds. Fairly compatible with set top boxes. Expensive media. |
Fun facts - CD-R colors - Which is better?
Discs come in many different colors. The color you see is determined by the color of the reflective layer (gold or silver) and the color of the dye (light blue, dark blue, green, or colorless). For example, combining a gold reflective layer with cyanine (blue) dye results in a disc that is gold on the label side and green on the writing side.
Green (average reflection, limited life)
Blue or gold (best reflection, long life)
Black (tinted poly)
The following effect the life expectancy of rewritable media:
- Radiation
- Inks or solvents
- Water, or pollutants (fungus)
- Extreme Temperature Conditions
Industry guidelines suggest testing at least every two years.
Physical hook up
- Master on secondary IDE - Very A+
-
Set via jumpers or
cable select
- Needs power
Logical hook up
- Device Manager Settings
- May choose drive letter even in Win9x
- Booting to floppy will require CDROM drivers
Pretty CD looking… - Very A+
Optical drives can be internal or external affairs, but whether internal or external, they have to somehow connect to the bus system of your PC. It turns out that there are several ways to jack your optical drive into your system.
- Audio card with CD-ROM interface – of historical interest only
- IDE / ATAPI
- SCSI or Parallel or USB or Firewire
File systems add commonality between platforms
CDROM - IS0-9660
DVD - Micro-UDF and UDF-Bridge
Care and feeding
-
Clean disks from the
center out with a clean cloth
- Moves dirt off the medium
- Any scratch will run perpendicular to track not along it
- It is suggested that you use the eject button (or menu selection) to open and close the tray
- Don’t blow into an optical disk mechanism – moisture and saliva may decrease laser effectiveness. Use compressed air
- You may use a paper clip inserted in the emergency release hole (small hole in the front of the tray) to open a tray